Development in light-emitting diode (LED) lighting technology continues to take place at a dramatic pace. With improved brightness, lower energy consumption and longer life spans, the global market for LED lighting has grown exponentially. The rapid adoption of LED lighting in the commercial and residential markets requires further improvements in LED efficiency and quality. One of the important measurements for LED lighting is its long-term reliability, especially for high power LEDs, which operate under stringent condition and long hours.
To improve efficiency of the LED, highly reflective substrates are widely used for high performance LED packages and modules, especially in chip-on-board (COB) LED packages. However, the highly reflective substrate suffers from long-term reliability issues that reduce the life span of the LED device. For example, silver (Ag) is widely used in package substrates due to its high reflection. Traditionally, Ag is plated on a substrate such as an aluminum sheet. The plated Ag offers high reflectivity and improves the efficiency of the LED. However, Ag is a material that can easily migrate, be oxidized, and thus tarnish during the operation. Moreover, the speed of degradation of Ag accelerates dramatically with higher temperature. In an LED device, LED chips are attached to the highly reflective layer. The LED chip is the light source as well as the heat source in the LED package. When in operation, the LED chip generates heat and raises the temperature of the reflective layer surrounds it. The closer to the LED chips, the higher temperate is the substrate of LED package, and the faster for the substrate to degrade.
To slow the silver layer degradation, there has been development in new technologies to protect the reflective layer of the LED package. However, all the protection techniques treat the whole substrate uniformly without considering different temperature distribution and its effects in different areas of the substrate and they require additional steps to protect the substrate. These new protection technologies although prolongs the life span of the LED package, they fail to extend protections to the vulnerable areas, resulting in limiting the overall life span of the LED package.
A design for an LED packaging is sought that improves its performance and long-term reliability.